DNA double strand breaks are important lesions induced by irradiations. Random breakage model or quantification supported by this concept is suitable to analyze DNA double strand break data induced by low LET radiation,but deviation from random breakage model is more evident in high LET radiation data analysis. In this work we develop a new method , statistical fragmentation model , to analyze the fragmentation process of DNA double strand breaks. After charged particles enter the biological cell, they produce ionizations along their tracks, and transfer their energies to the cells and break the cellular DNA strands into fragments. The probable distribution of the fragments is obtained under the condition in wh ich the entropy is maximum. Under the approximation E≈E0+E1l+E2l2, the distribution functions are obtained as exp( αl+βl2) . There are two components, the one proportional to exp(βl2)，mainly contributes to the low mass fragment yields, the other comp onent, proportional to exp(αl)，decreases slowly as the mass of the fragments i ncreases. Numerical solution of the constraint equations provides parameters α and β. Experimental data , especially when the energy deposition is higher, sup port the statistical fragmentation model.
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